The present invention relates to brush seals for preventing oil mist generated in a bearing cavity from passing outwardly of the bearing cavity and particularly relates to brush seals having highly flexible, densely packed bristles for engaging a rotary component for effectively maintaining the oil mist within the bearing cavity.
Rotating machinery generally includes a first rotary component such as a shaft rotatable relative to a fixed component, e.g., a housing. The shaft is typically rotatable in one or more bearings fixed to the housing. The bearings include a bearing cavity and generally include an oil film. The rotary movement of the shaft within the bearing cavity generates an oil mist which must be prevented from leaving the bearing cavity. Otherwise, the oil mist may settle on other parts of the rotary machine which may cause damage to the machine. Also, oil mist flowing from the bearing cavity may settle out in the surrounding environment, causing a safety hazard and, of course, an unpleasant aesthetic condition.
In many rotary machines, simple tight clearance seals, where the stationary component fits tightly about the rotating component, are sufficient to prevent the oil mist from migrating from the bearing cavity. However, in certain applications, large rotor radial excursions may occur. Consequently, the tightness of the clearance seals is a function of the radial excursion of the rotor. To accommodate such excursions, adequate spacing between the rotary and fixed components at the seal is necessary, oftentimes leaving sufficient clearance for the oil mist to flow or migrate from the bearing cavity through the clearance opening. Another seal commonly used to contain oil is a labyrinth seal. A labyrinth seal comprises a plurality of axially spaced teeth projecting essentially radially from the fixed component, the teeth being either machined or added as inserts into the fixed component. Because these teeth have a relatively small axial dimension and generally are formed of softer material than the rotating component, damage to the rotating component is unlikely in the event of a radial excursion. It will be appreciated that the tortuous path between the rotary component and the teeth of the labyrinth seal creates a seal at least as effective as a simple clearance seal. However, in the event of large or significant radial excursions, the labyrinth seal teeth are damaged and, once damaged, irreversibly provide for an increase in leakage flow over the remaining useful life of the seal. Further, in most implementations of labyrinth seals, the seal involves a large complex casting requiring a significant amount of machining to form the seals. Also, the mass of these labyrinth seals can be extensive, rendering assembly difficult. Accordingly, there is a need for an effective, low-cost seal for sealing a bearing cavity to prevent or minimize leakage of oil mist and which seal avoids machining complexity typical of seals employed for a similar purpose.
In accordance with a preferred embodiment of the present invention, there is provided a rotary machine having a rotatable component such as a rotor and a fixed component such as a housing having an oil bearing including an oil bearing cavity. The oil in the cavity generates an oil mist which is sealed in the cavity on one or both sides of the rotary component by a brush seal. The brush seal may comprise the sole seal for sealing the bearing cavity or it may comprise a brush seal in combination with one or more labyrinth seal teeth or with another brush seal. Each brush seal includes a backing from which projects a plurality of brush seals, the tips of which lie in engagement with the rotary component. Because the sealing environment for preventing oil mist from migrating from a bearing cavity is a low pressure environment, i.e., a nominal or minimum pressure differential across the seal, the bristles of the seal may be formed of a very flexible material to accommodate radial excursions of the rotary component. Additionally, the cant angle of the bristles, i.e., the angle of the bristles relative to a radius, may be small as compared with conventional brush seals, i.e., on the order of about 5-10xc2x0. The bristles are preferably formed of a polymer material.
In a preferred form of the present invention, the brush seal is mounted on a sheet metal backing plate which can be affixed to the fixed component. For example, two arcuate sheet metal plates, each extending approximately 180xc2x0, carry the backing plates confining the bristles of the brush seal along a radial innermost edge. The sheet metal support is simply bolted to the housing. By forming the brush seal support of sheet metal, the construction is much lighter, does not require extensive machining, and simplifies installation yet retains all of the benefits of a brush seal. Additionally, with this type of construction, the brush seal can be applied as a retrofit onto existing seals. For example, one or more labyrinth seal teeth can be removed from existing seals and replaced by the brush seal in a low-cost manner. It will be appreciated that a brush seal of this type may be used in virtually all the forms of rotating machinery, including gas turbines, steam turbines, compressors, motors and the like, where a seal for an oil bearing cavity is necessary. It will also be appreciated that because of the low pressure differential across the seal, the brush bristles can be formed to a much smaller diameter than the diameter of conventional brush seal bristles and, consequently, a highly dense packing of the bristles can be provided.
In a preferred embodiment according to the present invention, there is provided a rotary machine comprising a rotatable component, a component fixed against rotation including a housing having a wall and a bearing in a bearing cavity on one side of the wall, the bearing cavity containing an oil mist generated by the rotation of the rotatable component in the bearing cavity, a seal between the rotatable component and housing wall for substantially sealing the oil mist in the bearing cavity from migration outwardly of the bearing cavity past the wall, the seal including a brush seal carried by the housing wall and having flexible bristles engaging the rotatable component, a backing plate for supporting the bristles and a sheet metal mounting plate carrying the backing plate for securement to the housing wall.